The Sirtuins are a conserved family of NAD-dependent protein deacetylases that function in a wide variety of cellular processes, including repression of gene expression (silencing), apoptosis, and lifespan regulation. The requirement of these proteins for NAD has led to renewed interest in the NAD biosynthesis pathways in yeast and other model organisms that are used as models for the study of aging and age-associated diseases. Dissecting these pathways is critical toward understanding how Sirtuins interact with the cellular environment and respond to changes in metabolism or stress. Recent work in the lab has revealed the existence of a previously uncharacterized pathway for nicotinamide utilization that feeds through the nicotinamide riboside pathway, and will be the subject of specific aim 1. We have also recently identified thiamine biosynthesis as a metabolic pathway controlled by the Sir2 and Hst1 Sirtuins in response to changes in NAD and nicotinamide concentrations. The interesting co-regulation of the NAD and thiamine pathways in relationship to aging is the subject of specific aim 2. In specific aim 3, we plan to continue the investigation of NAD and nicotinamide regulation of Sirtuins in the nucleus by identifying the genes that each of the yeast Sirtuins regulate at the transcriptional level. These studies are expected to spur the identification of new conserved NAD biosynthesis and Sirtuin targets for future development of age-related disease therapeutics. PUBLIC HEALTH RELEVANCE: The NAD-dependent protein deacetylases (the Sirtuins) play an important role in the regulation of lifespan in multiple model organisms, including the budding yeast, Saccharomyces cerevisiae. The goal of this research project is to better understand the pathways by which NAD is synthesized in both yeast and mammalian cells, and to determine what cellular processes related to aging are controlled by the Sirtuins in response to alterations in cellular NAD levels. The large amount of conservation between the yeast biosynthesis pathways and those in higher eukaryotes any findings in yeast applicable to mammals.